KR20050097927A - Rewritable optical record carrier - Google Patents

Abstract

A rewritable optical record carrier comprising a first substrate carrying a first recording stack of layers, which recording stack comprises, a first dielectric layer, a recording layer comprising a phase-change recording material, a second dielectric layer, and a metal mirror layer. In order to achieve a maximum difference between the reflection of the crystalline regions and the amorphous region, said first dielectric layer has a thickness d1 in the range of 20 nm to 50 nm, and said second dielectric layer has a thickness d2 according to the relation 0.0225*d22 - 2.6572*d2 + 173.3(nm) < d1 < 0.0225*d22 - 2.6572*d2 + 213.3(nm) when the mirror layer comprises aluminum, or a thickness d2 according to the relation 0.0191*d22 - 2.0482*d2 + 149.6 (nm) < d1 < 0.0191*d22 - 2.0482*d2 + 189.6(nm) when the mirror layer comprises silver.

Description

Rewritable Optical Recording Medium {REWRITABLE OPTICAL RECORD CARRIER}

The present invention relates to a rewritable optical recording medium having a substrate having a multi-layer recording stack (IPIM), the recording stack comprising a first dielectric layer (I ₁ ), a recording layer having a phase change recording material (PC) ( P), the second dielectric layer I ₂ and the mirror layer M composed of a mixture containing aluminum as a main component or a mixture containing silver as a main component are sequentially provided. The invention also relates to a rewritable optical recording medium having a recording stack (MIPI) comprising the layers in reverse order.

In all known recordable optical recording media such as CD-RW, DVD-RAM, DVD-RW and Blu-ray Disc (BD), a recording stack including a phase change (PC) recording layer is applied. The PC layer is typically sandwiched in a stack between en dielectric ZnS-SiO ₂ layers. An optional medium for erasable phase change recording is an alloy having a durable polycrystalline structure, for example an alloy composed of Sb and Te, in addition to an alloy composed of In, Ge, and / or Ag. A mirror layer is deposited on one side of such a recording stack, which is typically made of a metal such as gold, aluminum or silver. The recording stack is deposited on a substrate such as a polycarbonate substrate. The recording laser beam modulated by the recording signal entering the recording medium from the substrate is focused on the recording stack. While the disk is moving relative to the focused laser beam, the laser beam is mainly absorbed by the recording layer. Therefore, the alloy is locally heated. If the temperature exceeds the melting point (about 500 ° C. to 700 ° C.), the phase change material changes to an amorphous state. Rapid heat dissipation through adjacent dielectric layers causes the alloy to cool rapidly, thereby stabilizing the amorphous phase. Thus, the recorded mark remains along the track. The application of the laser beam at low power erases the recorded mark. Thus, the recording layer is heated (annealed) to a temperature of approximately 200 ° C. which induces a phase change to the crystalline phase. Since atoms must be kept at elevated temperatures long enough to harden, crystals are a rather slow process, although amorphousness in PC media can be very rapid.

The stack has high reflectivity in the crystalline phase (base state) but low reflectivity in the amorphous phase (record state). Therefore, the read beam focused on the recording stack is reflected by the recording layer at different intensities depending on whether the beam irradiates a recording mark (feet) or a non-recording region (land). Thus, the dielectric and reflective layers perform a number of tasks: protect the recording layer, create an optically tuned structure that optimizes the reflectance and / or absorbance, and match the thermal characteristics of the disc for rapid cooling. do.

Recordable optical recording media as well as general recording media have shown an evolutionary increase in data capacity, for example due to the explosive increase in the amount of data provided for multimedia applications. The data capacity of recordable optical recording media ranges from 650MB (CD, NA = 0.45, λ = 780nm) to 4.7GB (DVD, NA = 0.65, λ = 670nm), and finally 25GB (Blu-ray Disc (BD), NA = 0.85, λ = 405 nm). The data capacity can be further doubled by increasing the number of write stacks per disc. A so-called dual recording layer stack structure is known as a DVD-ROM. The two recording layers are arranged in a stack with spacers between the two recording layers on the same substrate. In this type of disc, the recording layer can be accessed from the same.

However, due to sufficient absorption of the laser light in the rewritable recording medium, it becomes more difficult to record or read information on the double recording layer stack in such a medium. The laser beam is the second recording stack L ₁ furthest from the advancing direction of the incident laser beam after a considerable amount of output is absorbed by the first recording stack L ₀ closest to the advancing direction of the incident laser beam. It must be strong enough to record it. Therefore, such a multilayer stack has not been defined so far for a rewritable optical recording medium.

At the same time as the demand for data capacity increases, the demand for high data rate in phase change optical recording is increasing. High data rates require a recording layer with a high crystallization rate, i. To ensure that previously recorded marks can be recrystallized during direct overwrite (DOW), for example, as described above, the recording layer is suitable to match the linear velocity of the recording medium rotating with respect to the laser beam. You must have a decision time. If the crystal velocity is not fast enough to match the linear velocity, data older than the previous record cannot be completely erased. The remaining old data fragments cause high noise levels.

Recently, in US Patent Application Nos. 2001-0036527, 2001-00365278, and 01/13370, to satisfy optical ranges prescribed by DVD-standards such as jitter, optical contrast and modulation even at high linear velocities. A rewritable optical recording medium having sufficient recording characteristics has been proposed. However, such a recording medium has an L ₀ recording stack having a transmittance of 40% to 60%. Since the laser power reaching the L ₁ to reduce as much as L _1, the recording stack are to be highly sensitive, particularly in high linear velocity. On the other hand, since the light of the read laser beam reflected from the second write stack L ₁ is attenuated once again on the way through the L ₀ stack to the detector, the L ₁ stack must have a very high sensitivity.

Therefore, it is an object of the present invention to provide a rewritable optical recording medium having a stack structure that provides good optical properties with respect to photosensitivity and reflectance.

According to the present invention, in a rewritable optical recording medium as described in the introduction having a recording stack having the layers in order (IPIM), the first dielectric layer has a thickness d ₁ in the range of 100 nm to 200 nm, wherein the second The dielectric layer is achieved by a rewritable optical recording medium characterized by having a thickness d ₂ according to one of the following relationships.

If the mirror layer comprises aluminum,

0.0225 * d ₂ ² -2.6572 * d ₂ +173.3 (nm) <d ₁ <0.0225 * d ₂ ² -2.6572 * d ₂ +213.3 (nm) (1)

If the mirror layer contains silver,

0.0191 * d ₂ ² -2.0482 * d ₂ +149.6 (nm) <d ₁ <0.0191 * d ₂ ² -2.0482 * d ₂ +189.6 (nm) (2).

According to a second aspect of the invention, in a rewritable optical recording medium as described in the introduction having a recording stack with layers in reverse order (MIPI), the first dielectric layer I ₁ has a thickness d _{1 in the} range of 100 nm to 200 nm. Wherein the second dielectric layer I ₂ has a thickness d ₂ according to formula (a) when the mirror layer comprises aluminum and according to formula (b) when the mirror layer comprises silver. This is achieved by a rewritable optical recording medium.

According to a third aspect of the invention, which constitutes an additional refinement of the first or second aspect of the invention, the second dielectric layer has a thickness in the range of 20 nm to 50 nm.

According to a fourth aspect of the invention, which constitutes an additional improvement of the first or second aspect of the invention, the first dielectric layer has a thickness in the range of 110 nm to 150 nm, and the second dielectric layer is in the range of 25 nm to 40 nm. Has a thickness.

While the development of a recording stack proposed for use in a conventional rewritable optical recording medium focuses on high optical contrast, the rewritable optical recording medium according to the present invention has a maximum reflection R * M (= R _c -R _a , crystalline A recording stack optimized for reflection R _c -amorphous reflection R _a ). As can be seen from the examples below, this results in a fairly high reflectance. In addition, the photosensitivity, which is the laser output required to record the mark, can be increased.

These and other objects, features and advantages of the present invention will become apparent from the description of the preferred embodiments in conjunction with the accompanying drawings.

1 shows a cross-sectional view of a conventional rewritable optical recording medium.

2 shows a cross-sectional view of a rewritable optical recording medium according to a preferred embodiment of the present invention.

3 shows a combination of I ₁ layer thickness and I ₂ layer thickness of a recording stack according to the invention with an aluminum mirror layer producing _a maximum of R _c -R _a .

4 shows a combination of an I ₁ layer thickness and an I ₂ layer thickness of a recording stack according to the invention with a silver mirror layer producing _a maximum of R _c -R _a .

5 shows the optical contrast of the reflected signal R _c , R _a , the difference R _c -R _a , and the reflected read beam as a function of the I ₂ thickness.

6 shows the optical contrast of the reflected signals R _c , R _a , the difference R _c -R _a , and the reflected read beam as a function of the I ₁ thickness.

Fig. 7 is a diagram showing modulation and jitter of a rewritable optical recording medium according to the present invention having a single recording stack depending on the recording output.

8 is a diagram showing modulation and jitter of a rewritable optical recording medium according to the present invention having two recording stacks depending on the recording output.

The conventional rewritable optical medium 10 shown in FIG. 1 has a single recording stack 101 fixedly disposed on a so-called dummy stack or dummy substrate 102. Here, all declarations about the position and / or direction of the layers and their arrangement relate to the direction of the incident laser beam indicated by arrow 110. The upper single write stack 101 also considered L ₀ is the stack closest to the inflow surface of the laser beam. As mentioned above, known recording stacks for reflectance and photosensitivity are not suitable for use in the lower stack L ₁ . Since the amount of light passing through the top layer 101 is small, it does not have sufficient photosensitivity to record the information and has a reflectance too low to read the information to the second level. Therefore, the dummy stack 102 is simply made of polycarbonate. The dummy stack 102 and the recording stack 101 are generally fixed by an adhesive layer and a spacer layer (not shown). The recording stack 101 includes a polycarbonate substrate 103, on which a first dielectric layer 104 is stacked. The layer 103 is made of a mixture of ZnS and SiO ₂ , for example (ZnS) ₈₀ (SiO ₂ ) ₂₀ and has a thickness in the range of 60 nm to 85 nm. The next adjacent layer is a recording layer 105 made of GeInSbTe, for example, having a thickness in the range of 12 nm to 18 nm. To the recording layer 105 on the opposite side of the first dielectric layer 104, a second dielectric layer 106 made of a mixture of ZnS and SiO ₂ having a thickness of 12 nm to 20 nm is attached. The bottom layer belonging to the L ₀ stack is a metallic mirror layer 107 made primarily of silver or gold. All layers of the recording stack 101 are stacked by sputtering in the above-described order to form an IPIM stack.

As shown in Fig. 2, the rewritable carrier 20 according to the present invention has a recording stack 201 as a second stack L ₁ with respect to the direction of the incident light beam, as indicated by arrow 210. On top of the L ₁ stack, a first transparent write stack L ₀ 202 may be deposited with a spacer layer (not shown) between the stacks 201 and 202. Such transparent recording stacks typically have a transmittance of 40% to 60%. As can be seen below, the L ₁ recording stack 201 according to the present invention other than the known recording stack due to high reflectance and photosensitivity is perfectly adapted to recording under the above conditions.

The L ₁ write stack 201 is a first (ZnS) ₈₀ (SiO ₂ ) ₂₀ dielectric layer 203, for example 12 ± 1.5 nm, referred to as I ₁ from top to bottom 100 to 200 nm, preferably 120 nm to 160 nm. And a recording layer 204 made of GeInSbTe having a thickness in the range. ₂₀ layers 205 of the second dielectric (ZnS) ₈₀ (SiO ₂ ), referred to as I ₂ , adjacent to the recording layer 204 opposite the first dielectric layer 203, which is 20 to 50 nm, preferably 25 to 40 nm. This exists. Underneath is a mirror layer 206. It is made of a metal or metal alloy, preferably aluminum, an Al mixture having a certain percentage of Ti, or gold. The mirror layer is typically about 50 nm thick. Finally, the bottom layer of the L ₁ recording stack 201 is a substrate 207 made of polycarbonate, for example. The above-described layer arrangement, i.e., the arrangement of the first dielectric layer 203, the recording layer 204, the second dielectric layer 205, and the mirror layer 2060, is stacked on the substrate 207 in the reverse order of the numerical representation, and thus the MIPI stack. To form.

The recording stack commonly used for the optical recording medium is not optimized for maximum reflection, in particular for reflection difference R * M (= R _c -R _a , crystalline reflection R _c -amorphous reflection R _a ). 3 and 4, the solid lines 301 and 401 represent the maximum reflectance difference for the recording stack each comprising the aluminum layer of FIG. 3 and the silver mirror layer of FIG. The combination of the I ₁ layer thickness and the I ₂ layer thickness of the recording stack according to the present invention should be selected along these maximum R _c -R _a lines 301, 401 which can be written by the following formula (where d ₁ is I ₁ layer thickness and d ₂ indicates I ₂ layer thickness).

a) for a reflective stack comprising an aluminum mirror layer

0.0225 * d ₂ ² -2.6572 * d ₂ +173.3 (nm) <d ₁ <0.0225 * d ₂ ² -2.6572 * d ₂ +213.3 (nm)

b) is for a reflective stack comprising a mirror layer

0.0191 * d ₂ ² -2.0482 * d ₂ +149.6 (nm) <d ₁ <0.0191 * d ₂ ² -2.0482 * d ₂ +189.6 (nm)

Since the I ₁ layer thickness in the conventional DVD ranges from 60 nm to 85 nm, R * M is far from optimal. In particular, R * M is small because the second dielectric layer thickness required for the disc type is in the range of 12 nm to 20 nm when a higher I ₁ thickness is required.

According to a preferred embodiment of the present invention, the I ₂ layer thickness for high reflectance and photosensitivity is selected to about 28 nm for a recording stack comprising an aluminum mirror layer and 25 nm for a recording stack comprising a silver mirror layer. . The corresponding I ₁ layer thickness for high R * M values is chosen to be about 135 nm and 130 nm, respectively. However, the I ₁ layer thickness may be chosen differently in view of other parameters such as photosensitivity, modulation or optical contrast, but should be kept within a range of ± 20 nm, which ranges from dashed lines 302 and 402 in FIGS. 3 and 4, respectively. And dashed lines 303 and 403.

In addition, the dielectric layer I ₂ 205 has a high thermal resistance because it is thicker than a conventional dielectric I ₂ layer (see FIGS. 1 and 2). Thus, heat transport from the phase change layer 204 to the mirror layer 206 is reduced. Since the mirror layer acts as a heat sink, smaller outputs are required to heat the phase change material to its melting point temperature. In this way a high photosensitivity of the recording stack according to the invention is obtained.

RTM measurement results of the second recording stack L ₁ in the recording medium according to the preferred embodiment are shown in FIGS. 5 and 6. According to this embodiment, the PC layer has a thickness of 12 nm. However, this can be chosen in the range of ± 1.5 nm, where the values of R _c and R _a hardly change. On the other hand, the difference in optical phase between the crystalline and amorphous (structural) states of the recording PC material varies dramatically within this range. This property can be used to optimize for push-pull variation. Al with 1.5% Ti added; The mirror layer used in this embodiment composed of the mixture is 50 nm thick. In FIG. 5, the difference and optical contrast of the focused reflection signals R _c , R _a , R _c -R _a are shown as a function of the thickness of the I ₂ layer. Therefore, the thickness of the I ₁ layer is applied in consideration of the maximum R * M value (see FIG. 3). In FIG. 6, the corresponding result is shown as a function of the thickness of the I ₁ layer and the thickness of the I ₂ layer is fixed at 28 nm.

The reflection of the crystalline phase R _c (diamond symbol) as well as the reflectance of the amorphous phase R _a (square symbol) decreases with increasing I ₂ (see FIG. 5), and therefore increases when selecting a thick I ₁ layer (FIG. 6). Reference). As can be seen from FIG. 6, an I ₁ layer thickness of 135 nm produces a maximum R * M, ie a maximum R _c -R _a (triangle symbol). According to FIG. 3, this value corresponds to an I ₂ value of about 28 nm. According to this, R * M can increase by more than 33%, whereas conventionally manufactured discs have 25%. Due to the rapidly increasing crystalline phase reflection R _c , the contrast (cross sign), which is the normalized reflection value, ie R _c -R _a divided by the crystalline phase reflection R _c , decreases to a value of 80% in this region.

The modulation and jitter dependence on the recording output of the laser beam in an optical disc according to another embodiment with a single recording MIPI stack L ₁ is shown in FIG. 7, whereby the laser beam is a polycarbonate dummy layer as an L ₀ stack. Through the L ₁ write stack. The same dependency on the recording output in a dual recording stack disk as proposed by the present invention is shown in FIG. 8, whereby the laser beam is a MIPI recording stack via IPIM recording stack L ₀ having a transmission of about 45%. Focused on L ₁ . The structure of the L ₁ stack in both recording media is as follows.

First dielectric layer: ZnS-SiO ₂ , 130 nm

PC recording layer: GeInSbTe, 12nm

Second dielectric layer: ZnS-SiO ₂ , 32 nm

Mirror layer: AlTi, 50 nm

From two recording experiments on the L ₁ stack as well as in the multilayer structure, the I ₂ thickness must be in the range of 20 nm to 40 nm to obtain accurate light sensitivity. On the other hand, below the above range, the recording output required for recording becomes high. Above this range, repetitive reading problems arise.

FIG. 7 shows that a low write power of about 12 mW is sufficient for writing when the disk includes a single L ₁ write stack with only a transparent dummy layer on top, thus obtaining 45% modulation and less than 10% minimum jitter. It can be seen that. If the proposed stack is so sensitive, it can also be used for a double layer disk as an L ₁ stack (see FIG. 8). With a reasonable write output of less than 30mW, low jitter and good modulation are obtained in this dual write stack structure.

It should be noted that the present invention is not limited to the embodiment described above. Other recording layer materials, dielectric layer materials, substrate materials and / or reflective layer materials may be used. In addition, the present invention is not limited to the optical recording medium having the dual recording stack structure as described above. It is also possible to provide a more compatible single layer optical recording medium of the IPIM type having the same optical properties and layer thickness as described above but having a single recording stack according to FIG. 2 deposited as a L ₀ layer on a dummy layer. In addition, a multiple recording stack structure may be provided having two or more recording layers having optical properties according to the present invention.

Claims (7)

A substrate having a first recording stack made up of a plurality of layers, The first recording stack is A first dielectric layer, A recording layer comprising a phase change recording material; A second dielectric layer, A rewritable optical recording medium comprising a mirror layer composed of a mixture containing aluminum as a main component or a mixture containing silver as a main component in the above order or in the reverse order. And the first dielectric layer has a thickness d ₁ in the range of 100 nm to 200 nm, and the second dielectric layer has a thickness d ₂ in accordance with one of the following relations. a) when the mirror layer comprises aluminum, 0.0225 * d ₂ ² -2.6572 * d ₂ +173.3 (nm) <d ₁ <0.0225 * d ₂ ² -2.6572 * d ₂ +213.3 (nm); b) when the mirror layer comprises silver, 0.0191 * d ₂ ² -2.0482 * d ₂ +149.6 (nm) <d ₁ <0.0191 * d ₂ ² -2.0482 * d ₂ +189.6 (nm). The method of claim 1, And the second dielectric layer has a thickness in the range of 20 nm to 50 nm. The method of claim 2, And the first dielectric layer has a thickness in the range of 110 nm to 150 nm, and the second dielectric layer has a thickness in the range of 25 nm to 40 nm. The method of claim 3, And the first dielectric layer and the second dielectric layer comprise a ZnS and SiO ₂ mixture. The method of claim 4, wherein And the phase change recording material comprises a mixture of Ge, In, Sb, and Te, wherein the recording layer has a thickness in the range of 12 ± 1.5 nm. The method according to any one of claims 1 to 5, A spacer layer attached to the first dielectric layer; And a second recording stack deposited on said spacer layer. The method according to any one of claims 1 to 5, And a dummy substrate deposited on said first dielectric layer.